Telephone trunking system.



Na. 845,452. PATENTED EEB. 26,1907.

F. -W.-DUNBAR.

TELEPHONE TRUNKING SYSTEM.

APP'LIGATION FILED AUG.23. 1902.

2 SHEETS-SHBBT 1.

rm: NORRIS PETERS ca., WASHINGTON, n c.

No. 845,452.- a PATENTEDFEB. 26 1907.

' P. 'WLDU-NBAR.

TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED AUG.23, 1902.

UNITED STATES PATENT OFFICE.

FRANCIS W. DUNBAR, OF CHICAGO, ILLINOIS, ASSIGNOR T O KELLOGGSWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

Specification of Letters Patent.

Patented Feb. 26, 1907.

Application filed August 23, 1902. Serial No. 120,768.

T0 00 whom, it may concern:

Be it known that I, FRANCIS W. DUNBAR, a citizen of the United States ofAmerica, and a resident of Chicago, county of Cook, and State ofIllinois, have invented a certain new and useful Improvement inTelephone Trunking Systems, of which the following is a specification.

My inventon relates, primarily, totelephone trunk-circuits and apparatuscooperating therewith, whereby telephone subscribers whose linesterminate at difierent central oflices or central stations may be'connected together for conversational purposes.

In common, battery telephone systems there are two main types ofcircuits employed. In both types the subscribers lines are provided atthe central oflice with a linesignal-controlling electromagnet and aconnection to the common battery, whereby when a subscriber desires tocall the central oflice he closes the limbs of the lines together at hisstation, preferably by taking up his receiver, thus completing thecircuit of the common battery through said electromagnet to operate thesame, and thereby indicate a call at the central office. The limbs ofthe telephone-line are also carried through the normally closed contactsof a cut.off relay at the central orlice, which relay when operatedserves to open the line to the battery, and thereby render theline-signal inoperative. In one type of circuits the winding of thiscutoff relay is entirely free from and unconnected with theline-circuit, while in the other type the winding of said relay isconnected with the line-circuit and is adapted to be operated by currentover a portion of the talking-circuit when a connection is establishedtherewith. In the former type of lines a third wire must of necessity becarried through the switchboard and be provided with a special contactin each of the springjacks or connection-terminals of the subscribersline. In view of this arrangement the said special contacts are made useof to determine the busy or idle condition of the subscribers line. Inthe other type of lines the cut-off relays are connected directly withthe talking-circuit and are energized over a portion of the same when aconnection is established, whereby the third wire throughout theswitchboard and the third contact of I the spring-jacks are dispensedwith. These lines are therefore termed two-wire lines.

My present invention relates to trunk-circults and apparatus wherebylines of the two different types may be connected together in suchmanner that the usual and best method of operating the trunk-circuitsbet-ween eX changes may be employed. The central o'l'lice at which thecall for a connection originates is known in telephonic parlance as theA or outgoing oflice and the trunks so used as the outgoing trunks,while the oflice at which the connection is completed is known as the Bor incoming office and the trunks as the incoming trunks.

The invention also consists of the features and arrangements hereinafterdescribed, and particularly pointed out in the appended claims.

My invention is illustrated in the accompanying drawings, in which thesame reference characters designate like p arts throughout the severalview s, and in which- Figure 1 is a diagram showing a trunking systemleading between two central oflxces, the subscribers lines at one ofhcebeing of the two-wire type, while the lines of the other office are ofthe type employing local ('lI'CL its for the cut-ofi' relays andtesting-contar ts. F ig. 2 is a similar view showing a slightircdification in the trunk and with sutscrilers lines at both ofhcesemploying local circuits for testing and for the cut-off relays. Fig. 3is a detailed view of the difi'erential supervisory relay employed.

Referring to 1* ig. 1, L designates one of the plurality of subscriberslines terminating at the central ofiice C. This line extends in twolimls 2 and 8 from the subscribers station A to the said central oflieeC, where it is fitted with suitable answering and multiple jacks orconnection-terminals J J At the subscribers station the usual telephoneinstruments are provided and consist of a transmitter 4, a receiver 5, aringer or callbell 6, and the condenser 7. The switchhook 8 is adaptedin its normal position and when the receiver is plat ed thereon to openthe circuit through the transmitter 4 and receiver 5 and to close itthrough the callbell 6 and condenser 7. A retardation-coil 9 isconnected at the substation when the hook is raised in parallel with thereceiver and condenser 7 to provide a path transparent to steadycurrents, but opaque to voice-currents 3 include, respectively, thearmatures or 5 springs 10 and 11' of the cutoil' relay R, which ispermanently legged to ground "from the sleeve-contacts j of the jacks JJ. The armature or spring 10 is normally connected with ground throughthe conductor I) 12, while the opposite armature 11 is normallyconnected with conductor 13, contain.- ing the line-relay R for theline, said conductor leading to the live or ungrounded pole of thecentral battery B, the opposite pole of which is grounded. Theline-relay R controls, through its armature, the circuit of theline-signal S. The forward contacts 14 and 15 of the cut-oil relay R areadapted to connect the jacks and the switchboardsection of the line withthe external line-cir cuit when the said cut-ofl' relay is energized.This, it is to be understood, is a typical two- Wire line-circuit and isthe particular kind With which I prefer to use my trunk-circuits,although I do not wish to so limit the use of the invention in allrespects. At the central ofl'ice C the usual operators cord-circuit isprovided, said cord-circuit having an answering-plug P and acalling-plug P, each being 0 provided with a tip-contact p and asleevecontact 9 adapted to register with like contact-suri'aces and j inthe acl s of the line when the plug is inserted therein. The tipcontaetsor the plugs are connected together 5 by means of the tip-strands t andt of the cord-circuit and the interposed condenser 0, while thesleeve-contacts are likewise connected by the sleeve-strands s and s andthe interposed condenser 0 A conductor 16 extends from the grounded poleof the battery B to the tip-strand t and contains the Winding of the tipsupervisory relay r associated with the answering-plug P, while the livepole of the battery is connected, by means of conductor 17, with theanswering sleeve-strand s and includes the winding or the sleevesupervisory relay 7". These re lays r and r" serve to control thecircuit of the supervisory lamp S associated with the answering-plug P,the "former relay serving to normally close said circuit of the lamp,While the latter relay normally opens the same. The battery 13 isassociated with the opposite or calling end oi the cordcircuit and isconnected by conductors 18 and 19 with the tip and sleeve strands t and8, respec tively, the former conductor including the winding 01 thesupervisory relay 7", while the latter conductor includes the similarrelay These relays serve, in a manner similar to the relays r and r, tocontrol the circuit of the supervisory lamp S, associated. with thecalling-plug P The relays r and r are conveniently referred to as thetip-relays, and relays r and l at their opposite terminais with the t Ihe line conductors 2 and eeaeee r as the sleeve-relays, since they mewere neeted with and operated by euri ent [h over the coriespondii;strands ol the circuit. The tip-str: 1 i t ol the caihn testing plug lis normally open through H extra spring or movable co i i-t it) atsleeve-relay 1' but ad aptei;

to be (lflf :l the said spring and its forward (0: isn't iii when therelay is energized. 'l he be. t tact 22 of this extra spring 20 is co";through the medium of co one side of the highv 1. inmedance relay 1-,inown as the lay, the other side ol which is groitmle i. The armatiue01'. this relayis likewise g= oufdt, ed, and its forward context is ccried .i .ih the primary Windin oi the op tion-coil 25 by me? ol eondother end of the said primary up i nected, through the 'inei'lium ol 0to the live pole ol the battery is", a .e tion-coil 27 being included inthis The operators transmitter its i one side to conductor 26, inlez'mezprimary coil and the coil 127,:i11d 1.11. the oi hz=- no side throughconductor :2) to giom il. condenser c is included i the operatic-k conduser a", in a bridge bet ol the cord-circuit by mean; key and indicateddis Branch connections 31 posite sides oi the re eiver and sero: an.order-hey 7;", rec ted with circuit or wire 33, h groundedalterii ator gis adapted to l resistance-hunt), with the tip-stii 1 H the stated g tothe cilia e t i'ii'm ewe e cord-circuit by means of the t spri g 7a, theSlCOYO-(K "art 01" s con? ected with batter, 26 and resistance 26 Atrunk-circuit is show tween the central ollices a d (r circuit beingtitted at the outg multiple jacks, such as J J or number. The tr .nlecreu t exte limbs 35 and 36 to the (e iral ollire '1" it is provided withsuitable means {or the condi n. of the wanted e, m the desiredsubscriber, and with sig able the operator to noper'iy atte; Y neetion.The tip and sleeve co and 236 terminate at the iatrot p the wi;:-.din.gsw and w' of the 1-epeatEn; y-

which are (OT-JEZQCiGll together thmuuzi *terposed conderser e The op in1 's w" and w of the said repeaii :l'

are ('(Ii'lllilhfifl together through the brim; B Which is common to theexrlta: e J to the incoming trunks at said excite...

sleeve strands t and s of the trunk-cord, which strands terminate in thecorresponding contacts p and p of the trunk-plug P. A trunk-relay r isconnected with the sleevestrand 86 of the trunk by means of conductor 37and upon the opposite side, by conductor 3S,with the spring-contact 39of the ditlerential supervisory relay r The normal contact 40 01' saidsprlng 38 is connected by conductor 41 with the tip-conductor 35 of thetrunk.

A disconnect-signal S and a ringingsignal S are provided for theincoming end of the trunk. The common conductor 42 leads to theindividual branches 43 and 44, containing these limbs, which branchesare again connected by a conductor 45, leading to the forward contact ofa grounded spring 46 of the difl'erential relay T In one of the par llelbranches the normal branch 43, containing the disconnect-lamp S and thearmature of the trunk-relay 1, is located and is so arranged as tonormally close the same. An additional grounded spring 47 is providedfor the differential relay r and when actuated makes contact with sprin39 of said relay and opens the circuit between the spring 39 and contact40. The operators receiver 48 is adapted to be bridged across thetrunkcord, together with the secondary of her in duction-coil 49 and acondenser c, by means oi a listening-key 7%, it being understood thatthese keys are only diagrammatic representations of any ordinarylistening-key, the springs of which are operated by a single lever orpush-button. The operators transmitter 50, which is in circuit with theprimary of the induction-coil 49, may be charged from the battery B orby means of a local battery.

An order wire or circuit 33 extends from the central oilice C to theo'flice C A ringing-generator g is adapted to be connected betweenground and the tip-spring 70 of the ringing-key, the sleeve-spring kthereof being grounded when operated. A resistancelamp 5] is placed inthe path of the ringingcurrent. The subscribers line L ternunating atthis oilice, is provided with a number of multiple jacks J J, each ofwhich has the usual tip and sleeve contacts and j and with thirdcontacts 7' which are adapted to be grounded when a connecting-plug isin serted in the ack. These springs 3' are connected with one side ofthe cut-oil relay R the opposite terminal of which is connected, bymeans of a conductor 52, with the live pole of the battery B Test-rings7' are provided for the several jacks and are insulated both when theline is not in use and during a connection. These rings are connected bya conductor 53 with the forward contact of spring 54 of the cut-offrelay, said spring being grounded through a suitable resistance 55. Aline-signal S is provided for the line I and is connected with the livepole of the battery by conductor 52 and at its opposite terminal withthe line conductor 3, which is normally open at the subscribers station.A bell 6 is provided at the latter station and is connected between thetip limb of the line and ground when the telephone is upon the hook 8,but is disconnected therefrom when the telephone is in use.

The operation is as follows: The A subscriber desiring a connection witha subscriber located at another exchange rernoves his receiver from thehook, and thereby closes a path for current between the limbs 2 and 3 ofhis line through the transmitter 4 and retardation-coil 9, the condenser7 and receiver 5 being connected in parallel with the retardation-coil.The closing of this circuit permits current to flow from the battery Bthrough conductor 18, line-relay 1x spring 11 of cut-oft relay R, limb 3of the telephone-line, through retardation-coil 9 and transmitter 4 atthe substation and thence over limb 2 back to the central oflice, andspring 10 cf ctt-ofl relay R, through conductor 12, to ground. Theline-relay R is thus operated and closes the circuit of the signal-lampS to ground from the conductor 13. The operator upon seeing the line-sinal exposed inserts the answering-plug P into the a swering-jack J ofthe subscribers line and connects her telephone t0 with the cord,circuit by depressing the listening-key 7c 70 to receive the order fromthe subscriber. The ins rtion of the plug P closes a circuit thro gh thecut-off relay R from the live pole of the battery B through condtctor17, sleeve superi isory relay 1 sleeve strand 8, sleeve-con acts 1)" andj of the plug and jack, thence th; u h the wincin; of the cut-off relayR to ground. The operation of this relay disconnects the armatures 10and 11 .rom the ground-wire 12 and from the battery-re d 13 and connectsthem 1h; ough the tor-ward contacts 14 and 15 of said armatures to thenormally disconnected jacks J J. lie operation of the supervisory relay1 over the path just traced serves to close, through its armature and trnt contact, the circuit of the stipervisory signal S which is associatedwith the 1; l; g r but it is prevented from glowing by the operation ofthe tip supervisory relay W, a hich is connected in the conductor 16 andreceives current over telephone-line and the tip-strand t of thecord-circuit and through the conductor 16 to the grounded pole of thebattery B as soon as the cutotl relay R is operated. The supervisorysignal S therefore remains inert while the battery B furnishes currenover the metallic telephone-line for the operation of the supervisoryrelays and for conversation al purposes. The opera tors transmitter 28is receiving current at this tine from the battery B over the conductor26, through retardation-coil 27, thence through the trans'i-nitter 28,and over conductor 29 to ground. When sound Waves strike thetransinitter 28, the current flowing tl'ieiethrough is varied, whichcauses a variation oi the charge in the condenser c and a correspondingsurge of current through the primary or her iiuluction-roil These inducevoice-currents in the secondary, Which are transmitted to the line, andthe operator is therefore able to converse With the calling subscriber.

Upon learning that a subscriber in the exchange 0* is desired the Aoperator deeresses the order-key le to connect her telephone with theorder Wire or circuit 33 and repeats the number of the Wanted subscriberto the B operator, Whose head-teleplione 48 is per inanently connectedwith said order-n ire. The latter operator designates to the A operatorthe trunk to be used and proceeds to test the condition of the Wantedline vith the tip of the plug or the incoming trunk named. If the lineis idle, no click ill be received, for the reason that the test-rings jof the subscribers line are insulated from ground; but if the lineis'busy the test-contacts will be connected through resistance 55 toground, and since the tip-contact of the plug is connected with the livepole of battery is a complete circuit will be established and theoperator Will receive a click, owing to the variation or the charge ofthe condenser 0. Upon finding the line idle the plug 1* is inserted inone of the multiple jacks oi the line wanted. The A operator, havingreceived the number of the trunk to be used, inserts the calling-plug itof her cord-circuit in the jack of the trunk at her ection. Theinsertion of the plug P closes a circuit from the live pole of thebattery B at the A oilice through conductor 19, the sleeve supervisoryrelay 1' sleeve-strand s" of the cord-circiit, sleevecontacts of theplug and jack, and over the sleeve-conductor 3c of the trunk throughconductor 37, the trunlorelay r, conductor 38, spring 39 of relay r andspring i? to ground. This circuit is established at the incoming end byreason of the plug P having been inserted in the jack of the line,whereby a path for current from the live pole of the battery B" isestablished over the the-strand oi" the trunk-cord and tip side of thesubscribers line and thence tarough the grounded signaling-bell at thesubstation. This op- GIiLtBS the ditlerential relay r and closes itssprings 46 and 47 upon their forward contacts. By means oi the currentin the path over the trunk just traced the supervisory signal S i:1 thecord-circuit is operated, and thus indicate to the A operator that thecalled subscriber has not yet responded. l he actuation of differentialrelay r at he incoming end connects a ground upon the llll'll) branchesbut as the trunk-relay r is operated When the lamp S lights it indicatesto the B operator that the called subscriber has not yet replied. 111calling the sulzsciilzer at the station D the ringingdroy 76 76 is dipressed, which sends current over the tip side of the line and throughthe grounded signaling-bell. In. case of the response of the calledsubscriber during ringing the groiuuhd hey it in the sleeve-strand ofthe trunk-cord provides a ready path to earth for the lt tirnringing-current. Upon the response oi the called shbszriher the t .vo li:nbs oi the metallic circuit are closed togc ther, and current from thebattery B ilons over the metallic line,

the transmitter at the station D and at the same time closing theniagi'ujtic e lects oi' the differential relay 1", which consequentlyroleases its springs 46 and -l7, the Former serring to open the circuitof the l'ii'iging-lninp it", to thereby extinguish it and indicate tothe B operator "hat the called subscriber has respondcd, uhile the otherspring l? peril its contacts 39 and 4-0 to close together, and thusconnect the trunk-relay r of the nutallic (ircuit oi the trunli, wherebycurrent is alien id to flow over the metallic circuit oi the trunk fromthe battery B and since the said trunk relay is o1 low resistance it isniainteinrd tittuated during conversation and the same time permits asu'llicient lion oi current to energiiae the tip supervisory relay r inthe It. (or(,lcirci.it, which serves to extinguish l io supervisory lampS to indicate to the j operator that the called subscriber has res; on:led. The S'LllJSGIillKlS are now connechd together "for conversation.The latt'; furnishing current to the line L for tell ing purposes andfor the operation ol the ('1 t-oll relay and supervisory relays. Thelottery B is furnishing current for the operation ol" the trunk andsupervisory relays, \i'hilo the battery B" provides the called line ithtalliing-curront and serves also to operate the several relays. Theringing-lamp 3 is n vented from operating by the clecnergixalion ofdi'l'l erential rclaji' r, \\"l.ile the disconnrcllamp has its pathopened at a second point by the trunk-relay r Upon. the to 'mination ofthe COHVUl'l-ltll ion the sutscrihers telephones are returned in theirbooks, with the result in ti 1 use oi" line L that the supervisorysignal S is operated, and at line L" the di'll'erential relay 1- is openated ly reason of the path for currrnt l b ing estatlished over the tipside oi the line through the grounded signaling-tell. Thus the actuationof dill'ercntial relay opens the metallic circuit of the trunh-lino tothrrely render the tip supervisory relay in the cord-circuitinoperative, which closes the circuit of the supervisory signal S" andlights it. 'i his indicates to the A operator the hanging up of the Dsul scrile "s tcle iihono. .l he cord-circuit is then disconnected fromthe thus furnishing current for the operation oi i trunk and thesubscribers line, thus restoring all parts to normal position at the Aoffice. The disconnection of the cord-circuit deenergizes thetrunk-relay r at the incoming end, which closes the circuit of thedisconnect-lamp S and causes it to indicate the fact of thedisconnection at the A office. The B operator upon seeing signal Stherefore takes down the connection at her office, thus restoring allparts to normal position.

Fig. 2 shows specifically the same arrangement at the incoming ofhce,the subscrib ers line L being the same and the trunk-circuit being thesame, except that the trunk-relay is adapted to be connected between thetip side of the trunk-circuit and ground through the medium of thegrounded spring 47 of the differential relay r instead of beingconnected from the sleeve side, as in the case of Fig. 1. At the Aoffice the subscribers lines are of the type shown at L which is thesame as the line L at the B office and the parts have beencorrespondingly designated. The cordcircuit for use at this office is ofthe type employing differential supervisory relays-that is, the relaysare disposed with their windings in .the opposite sides of thecord-circuit. whereby when current flows over the metallic line saidrelays are irresponsive and the supervisory signals controlled therebyare inert but when current flows over one side of the line or a greaterportion flows over one side,

so as to unbalance the magnetic effects of the two windings, the saidtwo relays are energized and the lamps are lighted. The batteries B andB are arranged as indicated. and the windings 0 and 0 of therepeatingcoil 0 are arranged in inductive relation, while the windings 0and 0 are likewise situated. Vi hen the subscriber A calls the centraloffice, the line-signal S is operated by current over the metallic line.The operator inserts the plug P of the cord-circuit into theanswering-jack of the line, and thereby closes the local circuit of thecut-off relay R which is energized from the battery B. This disconnectsthe line-signal S and connects the test-rings of the jacks to ground.The supervisory signal S remains inert on account of the current flowingover the metallic line through the substation. In order to establishconnection with the trunk, the Aoperator inserts the plug P in one ofthe jacks thereof, and, 'as explained with reference to Fig. 1, the plugP of the line has already been inserted in the jack of the wanted line,whereby the differential relay r at the in coming end is operated. Apath for current.- is therefore established over the tip side of thetrunk and through the trunk-relay 1 to ground, the current in this pathserving to operate the differential supervisory relay r to close thecircuit of supervisory lamp S to thereby indicate that the connectionhas been made at the called end and that the subscriber-has not yetresponded. As soon as the called sulscriter responds the metalliccircuit of the trunk is completed, which permits current from thebattery B in the A cord-circuit to flow over the metallic circuit of thetrunk to thereby render the differential supervisory relay rinoperative. .The supervisory signal 8 is rendered inert and indicatesto the A operator that the called subscriber has responded. Theremainder of the operation is the same as described w ith reference toFig. 1 and is not deemed necessary to repeat. The several parts of theapparatus have been designated by the same reference characters as inFig. 1, so that the operation will be readily understood.

Fig. 3 shows the superposed windings of the differential relay, such asis used in both the cord-circuit and trunk of Fig. 2 and the LlllIlk ofFig. 1,' these windings being superposed for the purpose of renderingthem'neutral to the. rapidly-varying voice-currents and at the same timepermitting theoperation of the relay when current fiows through onewinding only.

The ground connections heretofore referred tomay and in practice usuallyare one and the same, or they may be the common oliice-return. It isalso apparent that the other poles of the batteries may be 5 grounded sofar as the general operation of the system is concerned, it being onlynecessary to reverse the connections from those shown in the drawing. Itis also apparent, so far as some features of the invention areconcerned, that the lines may terminate in single cords and plugs inplace of the double cords shown and described and that the trunks mayterminate in jacks in place of plugs and cords.

While I have described one method of carrying out the invention, I wouldhave it understood that the said invention is not to be so limited, asit is apparent that various changes and substitutions may be madetherein and still come within its scope and principle; but

Vi hat I do claim as my invention, and desire to secure by LettersPatent, is

1. The combination with a trunk-line, of a cord-circuit to connect withits outgoing end and a called-subscribers line with which its incomingend is connect-ed, .a disconnect signal for said incoming end, meansoperated by current flowing over the called-subscribers line whenconnection is made therewith for placing said signal in condition tooperate,

and further means controlled by the connection of said cord-circuit withthe trunk for rendering said signal inoperative, substantially asdescribed.

2. The combination with a trunk-line, of a cord-circuit to connect withits outgoing end and a called-subscribers line with which its 1ncom1ngend is connected, a disconnect-signal for said 1ncom1ng end, meansoperated by signal being placed in operative condition by currentflowing over said side of the trunk circuit to ground, a relay having awinding energized when the called subscriber responds for disconnectingsaid ground and connecting the two sides of the trunk together to permitcurrent to flow over b oth sides thereof, said flow of current servingto render the supervisory signal inoperative, substantially asdescribed.

12. The combination with a telephone-line adapted to connect with acord-circuit at its outgoing end and connected with a calledtelephone-line at its incoming end, of a supervisory signal associatedwith the cord-circuit and placed in condition to operate by cur rentflowing over one side of the talking-circuit when the cord-circuit isconnected with the trunk, a trunk-relay at the inconiing end ofthe trunkconnected between the said side and ground, and means to connect saidtrunk-relay in the nietallic circuit of the trunk when the subscriberresponds, said relay being of low resistance so as to permit asufficient flow of current in the trunk-line to render said supervisorysignal inoperative, substantially as described.

13. The combination with a trunk-line adapted to connect with a callingtelephoneline at its outgoing end and a called telephone-line at itsincoming end, of a disconnect-signal at the incoming end of the trunkplaced in condition to operate by current over a portion of thetalking-circuit when connection is established with the, called line, atrunk-relay actuated by current over the trunk as long as the connectionexists at its outgoing end to prevent the operation of said signal,substantially as described.

14. The combination with a trunk line adapted to connect with a callingtelephoneline at its outgoing end and a called telephone-line at itsincoming end, of a disconnect-signal at the incoming end of the trunkplaced in condition to operate by current over a portion of thetalking-circuit when connection is established with the called line, atrunk-relay actuated by current over the trunk when connection isestablished with the line, and means for maintaining said relay actuatedduring conversation, said relay serving when energized to prevent theoperation of said signal, sub stantially as described.

15. The combination with a trunk-line adapted to connect with a callingtelephoneline at its outgoing end and a called telephone-line at itsincoming end, of a disconnect-signal for said incoming end placed incondition to operate by current flowing over a portion of thetalking-circuit when the trunk is connected with the called line, andmeans actuated by current iiowing over one side only of the trunl-:lineto prevent the actuation of said signal when the called-subscriber'stelephone is not in use and the conlnection exists at the outgoing endof the trunk, sus'istantially as described.

16. The combination with a trunk-line adapted to connect with a callingtelephoneline at its outgoing end and a called telephone-line at itsincoming end, of a disconnect-signal for said incoming end, meansoperated by current flowing over a portion of the talking-circuit w henconnection is made with the called line for placing said signal incondition to operate and further means controlled by the connection atthe outgoing end of the trunk for rendering said signal inoperative,said latter means being operated by current over one side of the trunkand ground, substantially as described.

17. The combination with a trunk-line adapted to connect with a callingtelephoneline at its outgoing end and a called telephone-line at itsincoming end, of a disconnect-signal for said incoming end placed incondition to operate by current flowing over a portion of thetalking-circuit when the trunk is connected with the called line, andmeans to prevent the actuation of said signal during such connection andw hen the callingline is connected with the trunk, said means beingactuated by current over one side only of the trunk when thecalledsubscribers telephone is not in use and over the metallictrunk-line during conversation, substantially as described.

18. The combination with a trunk-line adapted to be connected with acalling telephone-line at its outgoing end and a called telephonedine atits incoming end, of a disconnect-signal for said incoming end, meansorezated by current over a portion of the talking-circuit whenconnection is made with the called line -for placing said signal incondition to operate, and further means controlled by current sent overthe trunk-circuit when the calling telephone-line is connected with thetrunk for preventing the actuation of said signal, said latter meansbeing operated over one side of the trunk and ground when thecalled-subscrib ers telephone is not in use and over the metalliccircuit during conversation, whereby said signal can only be operatedwhen the said connection is severed at the outgoing end, substantiallyas described.

19. The combination with a trunk-line adapted to connect with acalling-line at its outgoing end and a called telephone-line at itsincoming end, of a disconnect-signal for said incomin end, meansactuated by current flowing over a part of the talking-circuit whenconnection is established with the called line for controlling thecircuit of said signal at one point to place it in condition to operateand further means governed by the connection of the calling-line withthe trunk and operated over one side of the trunk and ground forcontrolling the circuit of said sig- ICC nal at another point to preventits operation, substantially as described.

20. The combination. with a truqlscirouit adapted to connect at itsoutgoii-g end with. a calling telephone-lire and at its incoming endwith a called telephone-line, of a disconne" signal for said incomirplated in c n 7 tion to operate by curt t tlowing over a portion of thet: liiilg- *ircuit when the trunk is connected with the calledtelephonedine, and a trunk-relay energized. by current .llowi g over oneside oi the trunk and ground when the Cttllzf l'OiQPllOilQ-lilfi isconnected *ith the OtlbQOllg ejld. of the trun and the calledsubscriberstelephone is not in use, and energized during conversation by curreitover the metallic circuit, d latter relay servii'ig wh energized to reder said signal inoperative, subst. ially as described.

21. The combination. with. a trun ;-circuit adapted to connect at itsoutgoing end with a calling te ephojedine ai l at its incon g end with acalled telephone-line, of a relay at the incoming end actuated bycurrent over a portion. of the talkingcircuit when. connection isestablished with the called line, a trunk-relay actuate by currert overthe trunk when. co ts at the outgoing end, ant Lal at the incomii .g endentirely controlled by said two relays to cause it to give discor tlication when. connection is severed at the outg g end and still existsat the incoming end, substantially as described.

22. The combination with a trunk-circrit extending between dillerentswitcl1boardsections and adapted to connect telephonelines together forconversation, of a sir-pervisory signal associated with the oittgoingend adapted to be operated by ClUlGIlt over one side or thetallring-circr it thereol" when. connection. exists therewith and to berendered inoperative by current over the :u etallic circuit thereof, arelay at the incon g end. of the trunk actuated when connection isestabl shed with the coded line to permit the flow of current over thsaid one side of the outgoing end, and means for perniitti g current toflow over the said nietallic ciici it of the outgoing end when thecalled party responds, substantially as described.

23. The con": ination with a tru1k-ci.rcrit extending between dill'erentswitchboard sections and adapted to connect telephonelines together forconversation, of a supervisory'sigiual associated. with the outgoing;end of the trunk placed ia condition to operate when a connection isestablished at said end by current over one side of the talkingcircnitof said outgoing end, a relay at the incoming end of the trunkcontrolling the circuit of the said oi tgcing end, said relay beingoperative when the connection is established with the called line andbefore the response of the called party and inoperative duringconversation, substantially as (le i'ihml.

24. The combination with a t. ii li-circiit extending between.dill'ercnt :erwitclibciiiilsections and adapted to coiir tcttelephonelines together for cenveitatioii, ot a FF. poivieory signalassociated with the ongoing end placed. in condition to operate when aconnection is established at said end, a relay at the incoming end ofthe trunk controlling the path for c'tirrent over the outgoing end, saidrelay liieing energized. when the connection is established with thecalled-s1; bscril iors line and deener ized when the called subscriberresponds to permit in the latte; coo dition a How of current over theoutgoing on d oi the trunk su'llicicut to render saiil stpci visorysignal inoperative, substantially as K tscribed.

25. The cen'ibination with a tronlt-rirccit extending between dill'erentswitrhboawh sections and adapted to connect telephonelines togetl'ier orconycrsation, ct tlitl')tltviscry signal associated with the outgoingend of the trunk placed in. condition to opcr ate by current {lowingover a portion oi" the talking-circuit when connection is est cl ilishodat said end, a relay at the incoming Lilt'l ot the trunk controlling thepath for coxrcnr over the outgoing end, said relay being enorgized whenthe connection is established wit h the called line to periiit currentto [low over the outgoing end of the trunk to acti'ate said supervisorysignal, and ireans for tllit 'iit l'fjlb ing said relay when. the calledsubscriber rcspends, whereby a low-resistarce path tor current over theoutgoing end ol. the trout: is completed to permit a s lliciout [low ol'current thereover to render the said H'lilifi'itlrhill' signalinoperative, substantially as (lest-til not 26. The combination with atronlc-circi.it extending between dilleieut switcliboa'rih sections andadapted to coiuicct telephonelines together for conversation, of asupervisory signal associated. with the outgoing end, anelectroinagi'ietic winding in the pat h of current over one side of theltlllilll.,' fll'(i it oi the outgoing end oi the lil uh to place saidsignal in condition to operate, a second wiztl ing in the path ofcrjrrent over the other tl'lt of said end to render said signalinoperative when energized, an clectronagnetminding at the inco'iringend energized when the counection established with the called line andwhen the called-partys telephone is not in so, to complete the path torcitrreut over the said one side of the outgoing end, and a secondelectronia :t-winding at the incoming end to be CIlG'l lZtXl when thecallczl party answers to c the completion ol' the path for current overthe said iretallic cit-cit. sol;- stazitially as described.

27. The coi'nbination with a tru "v extending between dill'erentswitchhoardsections and adapted to connect telephonetogether forconversation, of a supervisory lines together for conversation, of asupervisory signal associated with the outgoing end, a trunk-relay atthe incoming end of the trunk actuated by current from over the outgoingend when a connection exists at said latter end, a signal at theincoming end whose actuation depends upon said relay, a second relay atthe incoming end serving when energized to complete a path for currentthrough said trunk-relay over one side of the outgoing end and whendenergized to complete a path over the metallic circuit of the outgoingend, whereby a suitable actuation of the said supervisory signal issecured and at the same time the signal at the incoming end is suitablycontrolled by the trunk-relay, substantially as described.

28. The combination with a trunk-circuit extending between difiere'ntswitchboardsections and adapted to connect telephonelines together forconversation, of a supervisory signal associated'with the outgoingsignal associated with the outgoing end,- a trunk-relay at the incomingend of the trunk actuated by current from over the outgoing end when aconnection exists therewith, a signal whose actuation depends upon saidrelay, and a second relay actuated over one side of the calledtelephone-line and ground when a connection is established therewith tocomplete a path for current through said trunk-relay over one side ofthe outgoing end, said second relay being deenergized when the calledsubscriber responds to thereby cause the completion of apath for saidtrunk-relay over the metallic circuit of the outgoing end, whereby asuitable actuation of the said supervisory signal is secured and at thesame time the signal at the incoming end is suitably controlled b y thetrunk-relay, substantially as described. 4

31. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephoneend, a trunk-relayat the incoming end of the 1 lines together for conversation, of atrunktrunk actuated by current from over the outrelay at the incomingend adapted to be acgoing end when connection exists at said lattuatedby current over the trunk from the ter end, a signal at the incoming endwhose actuation depends upon said relay, and a second relay at theincoming end actuated by current over a portion of the talking-circuitwhen'connection is established with the called line to close the circuitof said trunkrelay over one side of the said outgoing end, said relaybeing rendered inoperative by current over the metallic circuit when thecalled party responds, whereby a suitable actuation of the saidsupervisory signal is secured and at the same time the signal at theincoming end is suitably controlled by the trunkrelay, substantially asdescribed.

29. The combination with a trunk-circuit extending between diflerentswitchboardsections and adapted to connect telephonelines together forconversation, of a supervisory signal associated with the outgoing end,a trunk-relay at the incoming end of the trunk actuated by current fromover the out going end when connection exists therewith, a signal whoseactuation depends upon said relay, and a second relay at the incomingend actuated by current over the called telephone-line before thesubscriber responds to complete a path for said trunk-relay over oneside of the outgoing end, said second relay being deenergized when thecalled subscriber responds to thus close a path over the metalliccircuit of the outgoing end for said trunk-relay, whereby a suitableactuation of the said supervisory signal is secured and at the same timethe signal at the incoming end is suitably controlled by thetrunk-relay, substantially as described.

30. The combination with a trunlvcircuit extending between diii erentswitchboard-sections and adapted to connect telephone-lines outgoing endwhen connection exists at said end, a second relay at the incoming endof the trunk controlling the circuit of said trunkrelay and suitablyactuated by current over the talking-circuit when connection exists withthe called line, and a signal at the incoming end controlled solely bysaid two relays, substantially as described.

32. The combination with a trunk-circuit extending between differentswitchboard-sections and adapted to connect telephone-lines together forconversation, of a supervisory signal associated with the outgoing end,a trunk-relay at the incoming end of the trunk actuated by current fromover the outgoing end when connection exists at said latter end, asignal at the incoming end whose actuation depends upon said relay, andof a differential relay at the incoming end of the trunk suitablyactuated when connection exists with the called line and serving tocontrol the circuit of the trunk-relay, whereby a suitable actuation ofthe said supervisory signal is secured and at the same time the signalat the incoming end is suitably controlled by the trunk-relay,substantially as described.

83. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a signal at the incoming end of the trunk, atrunk-relay at the incoming end actuated by current over 34. Thecombination with a trunk-circuit extending ietween diflerentswitchboardsections and adapted to connect telephonelines together forconversation, of a ditl'erential relay at the incoming end having awinding in each side of the tall ing-circuit and unresponsive to currentin the metallic line,

and a signal at the incoming end whose actnation depends upon saidrelay, substantially as described.

35. The combination with a trunk-circuit extending between di'l'lerentswitchboardsections and adapted to connect telephonelines together forconversation, of a supervisory signal associated with the outgoing end,a trunk-relay at the incoming end of the trunk actuated by current fromover the outgoing end when connection exists at said latter end, asignal at the incoming end whose actuation depends upon said relay, anda second relay at the incoming end having ditl'erential coils, one ineach side of the talking circuit, one of said coils being included inthe path of current over one side of the called line and through thegrounded signaling-bell branch when connection is made with the line,whereby the differential relay is actuated to close the circuit of saidtrunk-relay over one side of the outgoing end and when the called partyresponds the said (li'l'lerential relay is rendered inoperative tothereby close the circuit of said trunk-relay over the me tallic circuitof the outgoing end,whereby a suitable actuation of said supervisorysignal is secured and at the same time the signal at the incoming end issuitably controlled by the trunlcrelay, substantially as described.

36. The combination with a trunk-circuit extending between di'tlerentswitchboardsections and adapted to connect telephonelines together forconversation, of a disconnect-signal at the incoming end, adi'l'lerential relay having a coil in each side of the talking-circuitat the incoming end, said relay being actuated by current through one ofits coils when connection has been established with the called line andthe calledpartys telephone is not in use to place said signal incondition to operate and said relay being rendered inoperative bycurrent in the metallic line when the called party answers, and atrunk-relay actuated by current sent over the outgoing end of the trunkto prevent said signal operating when connection exists at the outgoingend. substantially as described.

37. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephone lines together forconversation, of a supervisory signal associated with the outgoing end,atrunk-relay at the incoming end of the trunk actuated by current fromover the outgoing end when connection exists at said latter end, asignal at the incoming end whose actuation depends upon said relay, and.a sec- I end relay at the incoming end having dill'ei ntial coils, onein each side of the talkingcircuit, one of said coils being included inthe path of current over one side of the called line and through. thegrounded signaling-bell branch when connection is made with the line,whereby the diil'l erential relay is actuated to close the circuit ofsaid trunk-relay over one side of the outgoing end and when the calledparty responds the said dil'l'erential relay is rendered inoperative tothereby close the circuit of said trunk-relay over the int. talliccircuit of the outgoing end, said (litterential relay also controllingthe circuit of the trunk-relay, whereby a suitable actuation ol the saidsupervisory signal is secured and at the sajne tine the signal at theincoming end is suitably controlled by the trunk-relay, substantially asdescribed.

38. The combination with a trunl'\:ci1'cnit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a disconnect-signal at the incoming end, a dillerentialrelay having a coil in each side of the talking circuit at the incomingend, said relay being actuated by current through one of its coils overone side of the called telephone-line to the substation and thencethrough the grounded signaling-bell to place said signal in condition tooperate, and said relay being rendered inoperative by current in themetallic line when the called party answers, and a trunkrelay actuatedby current sent. over the outgoing end of the trunk to prevent saidsignal operating when. connection. exists at the outgoing end,substantially as described.

39. The combination with a trunk-circuit extending between di'llerentswitchboanlsections and adapted to connecttelephonelines together forconversation, of a ringing signal for the incoming end of the trunk, arelay actuated by current over one side of the called line whenconnection is established therewith to place said signal in condition tooperate, and means actuated by current in the metallic line when thecalled party answers to render said signal inoperative, substantially asdescribed.

40. The combination with a trunk-circuit extending between differentswitchboard sections and adapted to connect telephonelines together forconversation, of a ringing signal for the incoming end of the trunk, arelay actuated by current over one side oi the called line and thegrounded signalingbell at the substation for placing said signal incondition to operate, and means lot rendering said signal inoperativewhen the called party responds, substantially 28 described.

41. The combination with a trunk-line extending between differentswitchboanl-sections and adapted to connect telephonedines together forconversation, of a riiiiging signal ICS for the incoming end of thetrunk, a relay actuated by current over a portion of the tip side of thetalking-circuit and called line to place said signal in condition tooperate, and means responsive to current in the metallic line when thecalled party responds for rendering said signal inoperative,substantially as described.

42. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a ringing signal for the incoming end of the trunk, arelay actuated over a portion of the talking-circuit and called linewhen connection is established with the called line to place said signalin condition to operate, and means for rendering said relay inoperativewhen the called party responds to thereby render said signalinoperative,substantially as described.

43. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a ringing signal for the incoming end of the trunk, arelay actuated over a portion of the talkingcircuit and called line whenconnection is es tablished with the called line to place said signal incondition to operate, and means for deenergizing said relay when thecalled party responds to thereby render said signal inoperative,substantially as described.

44. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a ringing signal for the incoming end of the trunk, arelay actuated over a portion of the talkingcircuit and called line whenconnection is established with the called line to place said signal incondition to operate, and means actuated by current in the metallic linewhen the called party answers for rendering said relay inoperative tothereby retire said sig nal, substantially as described.

45. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a ringing signal for the incoming end of the trunk, adifferential relay having a coil in each side of the talking-circuit,means for closing a path through one of the coils when connection isestablished "with the called line to operate the same and thereby placesaid. signal in condition to operate, said relay being renderedinoperative by current in the metallic line when the called partyresponds to thereby render said signal inert, substantially asdescribed.

46. The combination with a trunk-circuit extending between differentswitchboard sections and adapted to connect telephonelines together forconversation, of a ringing signal for the incoming end of the trunk, a

differential relay having a coil in each side of the talk1ng-c1rcu1t,means for closing circult through one of said coils and over one side ofthe called-line to ground at the substation when connection isestablished with the said line and the subscribers telephone is not inuse, to thereby operate the same and actuate the signal, said relaybeing rendered inoperative by current in the metallic line when thecalled party answers to thereby render the said signal inert,substantially as described.

47. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a trunkrelay at the incoming end of the trunk actuatedby current from over the outgoing end when connection exists at thelatter end, a signal at the incoming end whose actuation depends uponsaid relay, a second relay at the incoming end having differentialcoils, one coil in each side of the talking-circuit, a source ofcurrent, one of said coils being in the path of current from said sourceover one side of the talking-circuit when connection is made with theline, whereby the differential relay is actuated at such time, and meansfor including the said source of current between the said coils and inthe me tallic circuit of the called line when the called subscriberresponds, whereby the said relay is rendered inoperative and thesubstation-transmitter is charged for talking purposes, substantially asdescribed.

48. T16 combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephonelines together forconversation, of a disconnect-signal for the incoming end of the trunk,means actuated by current over one side of a called telephone-line toplace said signal in conditlon to operate, and means actuated by currentover the trunk from the outgoing end when connection exists with saidend to prevent said signal operating, substantially as described.

49. The combination with a trunk-circuitextending between differentswitchboardsections and adapted to connect telephone- 1 lines togetherfor conversation, of a disconnect-signal for the incoming end of thetrunk, means actuated by current flowing over one side of a calledtelephone-line to the substation and ground. to place said signal incondition to operate, and means actuated by current over the trunk fromthe outgoing end when connection exists at said end to prevent saidsignal operating, substantially as described.

50. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect telephone lines together forconversation, of a disconnect-signal for the incoming end of the trunk,

means actuated by current over one side of the called telephone-line andthrough the grounded bell the substation to place said signal in COllt.ition to operate, andineans actuated by current over the trunk from theoutgoing end when connection exists at said end to prevent said. signaloperating, substantially as do cribed.

5.1. The combination with a trunk-circuit extending between Citlerentswitchboardsections and adapted to connect telephone lines together forconversation, of a disconneot-signal for the incoming end of the trunk,means actuated by current over the tip side of the called telephone-lineand through the grounded bell at the substation to place said signal incondition to operate, and iineans actuated by current over the trunkfrom the outgoing end when connection exists at said end to prevent saidsignal operating, substantially as described.

52. The combination with a trunk-circuit extending between ditl'erentswitchboardsections and adapted to connect telephone lines together forconversation, oi a disconnect-signal for the incoming end of the trunk,a relay actuated by current over one side of the called. telephone-lineto place said. signal in condition to operate, and a second relayactuated by current over the trunk from the outgoing end when connectionexists at said end to prevent said signal operating, substantially asdescribed.

53. The combination with a trunlecircuit extending between ei'tl'erentswitchboard sections and adapted to connect telephonelines together forconversation, of a (inconnect-signal lor the incoming end oi the trunk,a relay actuated by current over one side of the called telephone-lineand through the grounded signaling-bell at the substation to place saidsignal in condition to operate, and a second relay actuated by currentover the trunk from the outgoing end when connection exists at said endto prevent theoperation of said signal, substantially as described.

54. The combination with a trunk-circuit extending between ditlerentswitchlmardsections and adapted to connect telephonelines together forconversation, of a disconnect-signal for the incoming end. of the trunk,a relay actuated. over a portion of the tip sice of the line to placesaid. signal in condition to operate, and a second relay actuated bycurrent over the trunk 't'ron'i the outgoing end to renter said signalinoperative, sul'istantially as described.

55. The combination with a trunk-c' su t extending between diflerentswitchboardsections and adapted to connect telephon lines together forconversation, of a ringing signal for the incoming end of the trunkplaced in condition. to operateby current over one side of the calledline to the substation means actuated. by current flowing over thenietallic circuit when the subscriljim responds for rendering saidsignal inoperative. substantially as described.

56. The combination with a trui'ilt-circu t extending between differentswitchboardsections and adapted to connect subscribers lines togetherfor conversation, of a supe visory relay at the outgoing end actuated bycurrent over said end and ground when connection is established at bothends of the trunk, a supervisory signal controlled by said relay, andnteans actuated upon the response of the called subscriber 'lordisconnecting said. ground. connection to render the supervisory relayand signal inoperative, sn 1 stantially as described.

57. The combination with a trunk-circuit extending between differentswitchboardsections and adapted to connect subscribe s lines togetherfor conversation, of a supervisory signaling device and a source oieurrent at the outgoing end. connected between ground and thetalking-circuit, a ground connection from said end at the incoming endof the trunk during connection wit h the called line to provide arcturnpath l'or current from said source and norms for disconnectingsaid ground connection when the called party answers, substantially as(lescribed.

58. The combination with a trunk-circuit adapted to connecttolephonelines togeth r for conversation, of a supervisory signalassociated with. the outgoing end. of the trunk placed in condition tooperate by cur-rein over the tip side only oil the trunk when connectionis established at said end and wiili the called line at the other end,and. ireaiis operated when a called party responds to porn it a flow ofcurrent over both sides i the trunk to thereby render the said signalinoperative, substantially as described.

59, The combination with a trunk: ircu i' adapted to connecttelephone-lines together for conversation, a supervisory signalassociated with the outgoing end of the trunk, an electroiragnet-windingenergized by cu rent flowing over one side of the trunk to place saidsignal in condition to operate when a connection is established at saidend. and means operated upon. the response of the called party to pernita flow of current over both sides of the trunk, and anelectromagnetwinding in the path of said latter current and adapted torender said supervisory signal inoperative, substantially as described.

60. The co'lnbination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signal associated with the outgoing end of the trunk, an electromagnetic devicehaving two windings, one winding being disposed in the pat h of currentover one side only of the trunk,

and through the grounded signaling-bell, and i and adapted whenenergized to operate said lOC signal, and means operated when the calledparty lesponds to permit a flow of current over both sides of the trunk,and a second winding of said electromagnetic device in the path of thelatter current and adapted when energized to render said signalinoperative, substantially as described.

61. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signalingdevice associated with the outgoing end of the trunk having twodifferential windings connected in the path for current over oppositesides of the trunk, a path for current being completed through onewinding and over the tip side of the trunk only when connection has beenestablished at both ends of the trunk, and means operated when thecalled party responds to permit a flow of current over both sides of thetrunk, and through the other Winding of said signaling device to therebyrender the signal inoperative, substantially as described.

62. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a trunk-circuit,asupervisory signal associated with the outgoing end of the trunk placedin condition to operate by current over the tip side of the trunk withreturn over a third conductor, the metallic circuit of the trunk beingopen to prevent a flow of current thereover, and means operated when thecalled party responds to disconnect said third conductor and completethe metallic circuit of the trunk to permit a flow of current thereoverto render said supervisory signal inoperative, substantially asdescribed.

63. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signalassociated with the outgoing end of the trunk, an electromagnet-windingconnected in the path of current over the tip side of the trunk andground, and adapted when energized to place said signal in condition tooperate, the metallic circuit of the trunk being open to prevent a flowof current thereover, and means operated when the called party respondsto disconnect the ground and complete the metallic circuit to permit aflow of current thereover, and a second electromagnetwinding at theoutgoing end, the path of the latter current being adapted whenenergized to render said supervisory signal inoperative, substantiallyas described.

64. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signalingdevice associated with the outgoing end of called party responds todisconnect the ground from the tip side of the trunk and to connect thetwo sides of the trunk together to permit a flow of current thereoverthrough the other differential winding of said signaling device, wherebythe signal is rendered inert, substantially as described.

65. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a supervisory signalingdevice associated with the outgoing end'of the trunk having difierentialwindings placed in the opposite sides of the talking-circuit andresponsive to current over one side of the circuit, the signal beinginert when current flows over both sides of the circuit, means fordirecting an excessive current through one winding when connection isestablished at the outgoing end to render the signal inoperative, andmeans actuated upon the response of the called subscriber for equalizingthe magnetic effect of the current through said coils when the calledsubscriber responds whereby the signal is rendered inoperative,substantially as described.

66. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a relay at the incomingend actuated over a portion of the talkingcircuit when the trunk isconnected with the called line, a trunk-relay at said end actuated bycurrent over the tip side of the outgoing end of the trunk only andground when the connection is established at the outgoing end and beforethe called subscriber responds, and a signal at the incoming end whoseactuation depends upon said two relays, substantially as described.

67. The combination with a trunk-circuit adapted to connecttelephone-lines together for conversation, of a disconnect-signal at theincoming end of the trunk, a relay at said end actuated over a portionof the talking-circuit to place said signal in condition to operate whena connection is established with the called line, and a trunk-relayactuated over the tip side only of the outgoing end of the trunk toprevent the operation of said signal, substantially as described.

Signed by me at Chicago, county of Cook, State of Illinois, this 29thday of July, 1902.

FRANCIS W. DUNBAR.

Witnesses:

ROBERT Lnwrs AMEs, G. BEDER.

